Protein kinases (“PKs”) are enzymes that catalyze the phosphorylation of hydroxy groups on tyrosine, serine and threonine residues within proteins. Phosphorylation of these hydroxy groups is required for the growth, differentiation and proliferation of cells. Thus, virtually all aspects of the cell life cycle depend on normal PK activity. In view of the criticality normal PK activity has on healthy cell functioning, it is perhaps not surprising that abnormal PK activity has been related to a host of disorders, ranging from relatively non-life threatening diseases such as psoriasis to extremely virulent diseases such as glioblastoma (brain cancer).
Among other categorizations, PKs can be divided into two classes, the cytoplasmic protein tyrosine kinases (PTKs) and the transmembrane receptor tyrosine kinases (RTKs). Briefly, the RTKs comprise a family of transmembrane receptors with diverse biological activity. The HER (human epidermal growth factor receptor) subfamily of RTKs includes EGFR (epithelial growth factor receptor), HER2, HER3 and HER4. These RTKs consist of an extracellular glycosylated ligand binding domain, a transmembrane domain and an intracellular cytoplasmic catalytic domain that can phosphorylate tyrosine residues on proteins.
Another RTK subfamily consists of insulin receptor (IR), insulin-like growth factor I receptor (IGF-1R) and insulin receptor related receptor (IRR). IR and IGF-1R interact with insulin, IGF-I and IGF-II to form a heterotetramer of two entirely extracellular glycosylated alpha subunits and two beta subunits which cross the cell membrane and which contain the tyrosine kinase domain.
A third RTK subfamily is referred to as the “platelet derived growth factor receptor” (“PDGF-R”) group, which includes PDGF-R-α, PDGF-R-β, CSFI-R, c-kit and c-fms. These receptors consist of glycosylated extracellular domains composed of variable numbers of immunoglobin-like loops and an intracellular domain wherein the tyrosine kinase domain is interrupted by unrelated amino acid sequences.
Another group, which, because of its similarity to the PDGF-R subfamily (and is sometimes subsumed into the PDGF-R subfamily) is the fetus liver kinase (“a”) receptor subfamily. This group is believed to be made up of kinase insert domain-receptor fetal liver kinase-1 (KDR/FLK-1, VEGF-R2), flk-1R, flk-4 and fins-like tyrosine kinase 1 (flt-1).
Still another member of the tyrosine kinase growth factor receptor family is the vascular endothelial growth factor (“VEGF”) receptor subgroup. VEGF is a dimeric glycoprotein similar to PDGF but has different biological functions and target cell specificity in vivo. In particular, VEGF is presently thought to play an essential role is vasculogenesis and angiogenesis.
Sunitinib is a multi-targeted RTK marketed by Pfizer Inc. under the brand name SUTENT®. Chemically, sunitinib's systematic name is “N-(2-diethylaminoethyl)-5-[(Z)-(5-fluoro-2-oxo-1H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-carboxamide” and its chemical formula is provided below.

In vivo, sunitinib inhibits cellular signaling by targeting multiple RTKs, including (VEGFRs) and PDGF-Rs. Both of PDGR-Rs and VEGFRs play a role in tumor proliferation and angiogenesis, and sunitinib's ability to inhibit these targets leads to cancer cell death and reduced tumor vascularization, thereby resulting in tumor shrinkage. Sunitinib also inhibits other RTKs, such as KIT, RET, CSF-1R and flt3, thereby potentially making it clinically useful in the treatment of patients suffering from other cancers.
Also in vivo, sunitinib is metabolized to form a des-ethyl of sunitinib, which is roughly equipotent as sunitinib and has the following structure:

Treatment with sunitinib (which results in, among other things, the equipotent metabolite des-ethyl sunitinib), however, is not without drawbacks, including hand-foot syndrome, stomatitis, and other toxicities.
Therefore, a need exists to provide compounds that can exert the same pharmacology sunitinib has in vivo, yet has an improved side effect profile. The present invention seeks to address this and/or other needs.